The present invention relates to a process for producing metallurgical coke from high volatile caking coal.
Metallurgical cokes are high quality blast furnace or foundry cokes characterized by relatively high strength and stability. These cokes are routinely formed by a high temperature carbonization of bituminous coal blends. A typical blend is composed of high volatile, highly caking bituminous coals, hereinafter referred to as "caking coals", and medium and/or low volatile bituminous coals, hereinafter referred to as "coking coals".
Presently caking coals account for approximately 80% of the world's known reserves of Carboniferous coals (see Fisher, A.D., Metallurgical Coals for the Future; Proc. of 23rd Canadian Conference on Coal, Ottawa, Canada, pp 45-68, September, 1971). Many coal-producing countries are rich in their supply of caking coals, but possess an inadequate quantity of coking coals for the metallurgical blends. Heretofore, it has been necessary to blend caking and coking coals in order to obtain the high strength necessary in a metallurgical coke. At the present state of the art, caking coals alone, when carbonized, produce a coke having an inadequate strength. It is not feasible to use coking coals alone to manufacture a metallurgical coke because of their scarcity, relative high costs, and particularly due to the high expansion pressure exerted on the walls of a coke oven during carbonization.
Thus there is a need for a feasible process for producing coke, usable as metallurgical coke, from caking coals.
Previous workers have observed a minute increase in the strength of metallurgical cokes manufactured from some charges which have been preheated to temperatures of about 300.degree. C. prior to carbonization. This increase in strength has been attributed to the removal of water during the preheating step (e.g. see Beck, K.B., Requirements of Coking Coals and How They are Affected by the Technical Development of Pig Iron and Blast Furnace Coke Production; 25th Canadian Conference on Coal, Victoria, September, 1973). A problem associated with this pre-heating treatment is the difficulty in obtaining a fast and uniform pre-heating of such large quantities of coal. Additionally there is a possibility of coal dust explosions resulting from the necessity of charging the coke oven with the hot pre-heated coal. Finally there are difficulties involved in transporting the coal between the pre-heater and the coke oven. These problems and difficulties appear to have prevented pre-heating from being applied commercially.